As you approach the entry barrier, a carrier will recognise your numberplate, which you'll give to us beforehand, and automatically open the barrier and print a ticket for you. Don't worry though, if anything goes wrong, you can press a button to enter manually. Keep hold of your ticket, then park up in any space and catch the free transfer bus to the terminal.
When you return, pick up your car and drive to the barrier. If your ticket has your booking reference printed on it, you can simply insert it into the barrier, which will allow you to leave. If not, you will need to press the call button on the barrier and the car park staff will help you.